Endogenous and exogenous dopamine depress EPSCs in rat nucleus accumbens in vitro via D1 receptors activation.

Apr 1, 1996The Journal of physiology

Natural and introduced dopamine reduce nerve signals in the rat reward system through D1 receptor activation

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Abstract

Dopamine reduces the amplitude of glutamate signals by 56% in rat nucleus accumbens neurons.

Dopamine at 30 microM significantly depressed glutamate signals recorded at holding potentials of -80 to -90 mV.
Selective D1 receptor agonists also reduced glutamate signals by 36-48%, while the D2 receptor agonist had no effect.
The D1 receptor antagonist completely blocked the effect of dopamine, indicating the involvement of D1 receptors.
Cocaine and amphetamine, both dopamine mimetics, decreased glutamate signals by 40% and 62% respectively in some tested neurons.
Elevating cAMP levels resulted in a reversible increase in glutamate signal amplitude, suggesting a different mechanism from dopamine's action.
The findings indicate that dopamine may attenuate synaptic transmission through presynaptic D1 receptor activation without involving cAMP.

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1. Whole-cell patch clamp recordings were made from nucleus accumbens neurones in slices of rat ventral forebrain. In the presence of picrotoxin (50 microM), the amplitude of 6-cyano-7-nitroquinoxaline-2, 3-dione-sensitive glutamate EPSCs, recorded at holding potentials between -80 and -90 mV, was reversibly reduced by 56 +/- 11% (n = 6) by dopamine (30 microM). The selective dopamine D1 receptor agonists SKF 38393 (10 microM) and SKF 81297A (10 microM), but not the selective D2 receptor agonist quinpirole (10 microM), also reversibly depressed the EPSC by 36-48%. The depression of the EPSC by dopamine was completely blocked by the D1 receptor antagonist SCH 23390 (1 microM), whereas the D2 antagonist (-)-sulpiride (1 microM) was without effect. 2. EPSCs were reversibly depressed by the dopamine mimetic psychostimulants cocaine (1-20 microM) and amphetamine (10-30 microM) by 40 +/- 16 and 62 +/- 9%, respectively, but only in about half of the cells tested (11/23 and 6/13, respectively). Their actions were completely reversed by SCH 23390 (1 microM), indicating that endogenous dopamine can also depress the EPSC via D1 receptors. 3. No discernable effects of dopamine, SKF 81297A, SKF 38393, quinpirole, cocaine or amphetamine were observed on membrane conductance or holding current (at holding potentials of -80 to -90 mV), suggesting that the depression of the EPSC was solely due to an action on presynaptic D1 receptors. 4. In contrast, agents that elevate intracellular levels of adenosine-3':5'-cyclic monophosphate (cAMP) (forskolin (1-10 microM), 3-isobutyl-1-methylxanthine (0.1-1 mM), rolipram (10 microM), and dibutyryl cAMP (0.5-1 mM)) caused a reversible increase in the EPSC amplitude (by 21-150%). Furthermore, in the presence of forskolin (10 microM), the ability of dopamine to depress synaptic transmission was unaffected. 5. Together these data suggest that both exogenous dopamine and dopamine released from intrinsic nerve terminals attenuate glutamate receptor-mediated synaptic transmission in the nucleus accumbens by presynaptic D1 receptor activation. The transduction mechanism underlying this effect does not appear to involve the formation of cAMP.

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Endogenous and exogenous dopamine depress EPSCs in rat nucleus accumbens in vitro via D1 receptors activation.

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